Importance of aging to dehydration shrinkage of human dentin

There is an increase in the mineral content of human dentin with aging. Due to the consequent changes in the mineral to the collagen ratio, this process may influence the degree of hydrogen bonding that occurs with the loss of water and the extent of shrinkage as a result of dehydration. Thus, the objective of this investigation is to quantify the differences in the dehydration shrinkage of human dentin with patient age. Specimens of coronal dentin are prepared from the molars of young (23 ⩽ age ⩽ 34) and old (52 ⩽ age ⩽ 62) patients, and then maintained in storage solutions of water or hanks balanced salt solutions (HBSS). Dimensional changes of the dentin specimens occurring over periods of free convection are evaluated by using the microscopic digital image correlation (DIC). The results distinguish that the shrinkage of the young dentin is significantly larger than that of the old dentin, regardless of the orientation and period of the storage. The strains parallel to the tubules increase with proximity to the dentin enamel junction (DEJ), whereas the shrinkage strains in the transverse direction are the largest in the deep dentin (i.e., near the pulp). The degree of anisotropy in the shrinkage increases from the pulp to the DEJ, and is the largest in the young dentin.